Worcester Greenstar 30si Combi Boiler, will I need to upgrade?

[fastliving]

I've got a relatively new (2014) Gas Worcester Greenstar 30si Combi Boiler, which I am perfectly happy with and never not had hot water/heating. It seems to cope very well with my 1 bathroom, 8 radiator semi-detached house, my house is/must be pretty well insulated because I pay below average bills on gas.

I am hoping to do a fairly big house extension this year, and would probably add another shower & 4/5 radiators.

No-one in my house has baths if that makes a difference, and I guess it will be fairly rare that 2 showers are going at the same time as we all have different schedules, but both showers will be used daily.

How do I find out if I will need a bigger/better boiler to cope with this? I have tried google, and this boiler is recommended for small/medium houses with 1 bathroom, but I can't find out about maximum radiators.
Obviously if I was buying one after the extension I probably wouldn't by this one, but I am wondering if I can wing it and see if it copes, or it definitely needs to be replaced with the building work, and I need to budget for that.
Is 2014 old in terms of combo boilers and I should just change it anyway? (I am the kind of person who only replaces things when they are completely knackered, so this goes against my nature, and I will need to be convinced to do this!)

Ring Worcester, they will tell you.
Best boiler advice we had was always buy one the next size up from what you need ours has the house warm in 10 minutes as its over size but was only about £100 more.

It's not about the number of Radiators you have, it's their total heat output.
The Greenstar 30si has a heating output of about 25 kW but will be listed in the manual. You would need to add up the total heat output of all your current radiators and see if there is any spare capacity left to cope with your planned exstention.

Thanks isitabird the boiler I have had 30kw output, but how do I find out the individual radiators output? They are just old fashioned normal rads?

<a class="break-all" href="https://www.google.com/url?sa=t&source=web&rct=j&url=www.domestic-gas.co.uk/documents/CE54.pdf&ved=2ahUKEwiwke_vi_rnAhUDhlwKHd86DA4QFjAAegQIARAB&usg=AOvVaw1ecHqCBnJz8MsG940ymJ-k&cshid=1583093817496" rel="nofollow" target="_blank">www.google.com/url?sa=t&source=web&rct=j&url=www.domestic-gas.co.uk/documents/CE54.pdf&ved=2ahUKEwiwke_vi_rnAhUDhlwKHd86DA4QFjAAegQIARAB&usg=AOvVaw1ecHqCBnJz8MsG940ymJ-k&cshid=1583093817496
If you use the attached sheet, it will tell you the output for a boiler that you will need once the extension is done. I personally wouldn't recommend a gas combi boiler for two or more bathrooms. You ideally take the fact that two showers are running at the same time, which a gas combi can't deal with

Thanks @Muchlywrong can you repost the link...original one isn't working

Sorry the link doesn't seem to work, may be best to search "energy savings trust boiler size calculator". It should be a pdf document. On all my training these days, it is what is recommended to help size the right output boiler for your house. If your boiler is the right size for your house, I wouldn't recommend changing it. 4 years isn't very old for a boiler and as long as it is serviced regularly, you should be getting 12 -15 years minimum of life.
Whatever you do, don't go for an oversized boiler as someone has recommended above. It wastes energy, lessens the life of your boiler and central heating components and is a waste of money.

Thanks Muchly!

You can work it out with online with thermal calculators . first find your boiler spec on-line it will give it in kW or btu maximum output . then workout every room size if external wall type of insulation windows etc in the thermal calculator in your house .each room give you a btu or kW add them all together then this will give you existing requirement to heat your house . you should have some spare left over . if this enough for your extension you can roughy guess the size . if it goes over your existing boiler output your boiler will struggle and be work harder to keep up .

Look in screwfix or toolstation catalogue for radiators and everyone will have it own btu or kW depending on the size . match them up to your radiator and it will give you a good idea if your existing radiators are the correct size output for existing rooms .

hot water is done in litres per minutes . this is the maximum flow out of the hotwater tap . these boiler will struggle to supply two hot water taps at the same time full bore . if you need two bathroom with possibly of two running hotwater item you need the highest LPM rate as possible if buying a new boiler .